1. Field of the Invention
This invention relates to a variable inductor in which the inductances of two coils vary complementarily in response to the displacement of a movable member. More particularly, it relates to a variable inductor which is used in, for example, a displacement-electricity transducer for converting the angular displacement of a throttle valve in an automobile or the like into an electric signal.
2. Description of the Prior Art
In recent years, with the development of the automobile industry, the exhaust gas emitted from the automobile engine has become a major social problem as a source of environmental hazards. It is, therefore, necessary to clean the exhaust gas by any method. As a temporary expedient, the catalysis method is considered.
As a radical measure, however, the development of a clean engine is needed. It is thought the first essential to clean the exhaust gas by controlling the explosion within the engine.
To this end, the rotary engine, etc., have been developed and are being put into practical use as the clean engines. These engines, however, are not perfect, either. In order to control the explosion itself so that the exhaust gas can be always kept completely clean, it is further required to adopt a centralized control system based on an electronic circuit arrangement including a minicomputer. In other words, in order to solve the problem of air pollution ascribable to the exhaust gas of the automobile, it is desirable that all the parts of the automobile can be electronically subjected to the centralized automatic control. In order that, as one measure for achieving the purpose, the amounts and proportions of fuel and air to be supplied into the engine may be maintained at the optimum states, it is earnestly requested to realize an electronic detection and control device which monitors and controls a fuel injector and an air intake controller for the engine. Especially, a device which accurately detects the displacement of a throttle valve for regulating the amounts of fuel and air in the automobile engine is earnestly requested.
Regionally, the automobiles are used extensively over cold districts to tropical districts. Further, the difference between temperatures at the starting and the steady running of the engine is large, and the service temperature range is as wide as -40.degree. C. to +120.degree. C. Regarding the environmental conditions of use, the automobiles are naturally placed under very severe conditions besides bad roads, dust, rain, and snow. The displacement detection device for use in the automobile engine need accordingly be a structure in which thermal resistance, vibration resistance, moisture resistance, corrosion resistance, etc., are carefully taken into consideration and which is capable of a high sensitivity detection of the displacement. Moreover, the displacement detection device need be simple in the structure in order to be inexpensive in production, and need be endurable in order to detect the displacement, frequently changing because of the use, repeatedly several million times.
As a device for detecting the amounts of fuel and air to be sucked into the engine of the automobile or the like, a number of devices relying on mechanical detection methods have heretofore been put into practical use. However, they are complicated in mechanism, and it is difficult to say that they attain a satisfactory precision. On the other hand, when a prior art displacement-electricity transducer is used as the detector without any modification, there are problems in points of the service temperatures of from -40.degree. to 120.degree. C., the endurability and the precision.
For example, when the displacement of frequent changes is converted into an electric signal by the use of a variable resistor, there is the disadvantage that, on account of the friction between a resistance body and a slider, the resistance body wears away to become unusable.